Clarification of the influences of superficial velocity Ug and particle diameter dp on the gas–solid flow characterizations in a rolling circulating fluidized bed (RCFB) by electrical capacitance tomography (ECT) method

Abstract

The influences of the superficial velocity and particle diameter on gas–solid flow characterizations in a rolling circulation fluidized bed (RCFB) are clarified by using the electrical capacitance tomography method. Gas–solid flow characterizations include the time-space averaged particle volume fraction ᾱz′, the time transition of the cross-sectional average particle volume fraction 〈α〉t, and the radial profile of the particle volume fraction 〈α〉r/R. Two kinds of particles are selected in the case that the particle diameter is 0.22 mm and the superficial velocity is set to 2.0, 3.0, and 4.0 m/s and in the case that the particle diameter is 0.45 mm and the superficial velocity is set to 3.0, 4.0, and 5.0 m/s. After analyzing the results, the main conclusions are able to be summarized as follows: First, when compared with the superficial velocity, ᾱz′ visualized from particle distribution images is much more influenced by the particle diameter. Second, the fluctuations of 〈α〉t and 〈α〉r/R tend to be more serious under the conditions of larger particle and lower riser’s height, which are able to be quantitatively explained by the fast Fourier transform of 〈α〉t and the spatial standard deviation 〈σs〉 of 〈α〉r/R. Consequently, a strategy to guarantee both particle distribution stability and particle distribution uniformity within the RCFB is proposed.